This non-provisional application incorporates by reference the subject matter of Application No. 2001-385959, filed in Japan on Dec. 19, 2001, on which a priority claim is based under 35 U.S.C. xc2xa7119(a).
(1) Field of the Invention
The present invention relates to a failure diagnostic system that determines whether an atmospheric pressure detecting device for detecting an atmospheric pressure and outputting a detection signal indicative of the pressure has failed or not.
(2) Description of Related Art
Conventionally, because the atmospheric pressure has no correlation with the engine operating condition, it is difficult to check whether an atmospheric pressure sensor (atmospheric pressure detecting device) operates adequately in the case where an engine is provided with only one atmospheric pressure sensor. Accordingly, a conventional failure monitor for an atmospheric pressure sensor determines that the atmospheric pressure sensor has failed if the atmospheric pressure sensor outputs a pressure outside the range of pressures that can be detected during normal driving. In other words, if the atmospheric pressure sensor outputs an unlikely pressure outside a normal detection range as in the case of breaking or short-circuiting. This conventional failure monitor, which determines whether the atmospheric pressure sensor has failed or not according to whether the atmospheric pressure sensor outputs a pressure outside the normal detection range or not, cannot detect a failure in the atmospheric pressure sensor in the case where an output value from the atmospheric pressure sensor is stuck within the normal detection range (i.e. an output is fixed at a predetermined value) or in the case where the responsiveness of the atmospheric pressure sensor to the atmospheric pressure has deteriorated when the atmospheric pressure sensor outputs a value within the normal detection range.
As an example of conventional failure diagnostic apparatuses for atmospheric pressure sensors, there has been known a failure diagnostic apparatus disclosed in Japanese Laid-Open Patent Publication No. 01-35053. This failure diagnostic apparatus determines that an atmospheric pressure sensor has failed if a variation in the atmospheric pressure corresponding to a distance traveled is greater than a set value corresponding to the same distance traveled.
The failure diagnostic apparatus disclosed in Japanese Laid-Open Patent Publication No. 01-35053, however, has the problem that it cannot accurately detect a failure because it determines that the atmospheric pressure sensor is normal even if it has failed, in the case where an output value from the atmospheric pressure sensor is stuck within the range between the maximum pressure and the minimum pressure, which are set in correspondence with the distance traveled, or in the case where the responsiveness to the atmospheric pressure has deteriorated. Therefore, the atmospheric pressure sensor is required to be capable of quick and rational failure diagnosis as for the atmospheric pressure sensor without errors, and improved failure diagnostic accuracy.
It is therefore an object of the present invention to provide a failure diagnostic system for an atmospheric pressure detecting device, which is capable of rationally determining whether the atmospheric pressure detecting device has failed or not, and with improved diagnostic accuracy.
To attain the above object, there is provided a failure diagnostic system for an atmospheric pressure detecting device which counts the number of operations of the device to be operated whose operating condition is controlled using an atmospheric pressure detected by the atmospheric pressure detecting device, stores information related to the detected atmospheric pressure, and determines that the atmospheric pressure detecting device has failed if a variation in the atmospheric pressure calculated based on atmospheric pressure related information stored before the number of operations reaches a predetermined number of times is equal to or less than a predetermined value.